1. Field of the Invention
This invention relates to the cutting of vegetation, and more particularly, it relates to the cutting of vegetation using a flexible, non-metallic cutting line extending from a rotating head into a cutting plane.
2. Description of Prior Art
Various types of devices have been proposed for many years to facilitate the removal of vegetation by mowing, trimming, edging and like cutting operations. In general, these devices have employed a metal blade to effect vegetation removal. Devices of this nature employ prime movers such as electric and gasoline motors. As a result, rotating metal blades can inflict serious and terrible injury upon the user.
In about 1960, there was developed in Europe a trimmer/edger unit employing a flexible polymeric line extending from a rotating head for cutting vegetation. This unit did not work properly because of several defects in structure and operating parameters. In the United States of America, practical vegetation-cutting devices using flexible, non-metallic lines carried upon a rotating head were developed. The devices are shown in U.S. Pat. Nos. 3,708,967, 3,826,068, 4,052,789, 4.054,992, 4,067,108 and 4,104,797. These patented devices have met outstanding success in that these American developments provide safer electrical or gasoline-powered tools for vegetation cutting, edging and trimming operations.
The devices shown in these patents employ a flexible cutting line such as manufactured from Nylon.RTM. polymer. The cutting line is carried usually upon a spool internally of a rotating head. When desired to replenish the line or to extend an additional length of it, the rotation of the head was stopped and line manually extended from the spool. This line-extension procedure in the patented devices has been found to be convenient, simple and reliable. In many of the more powerful devices, especially those powered by d.c. electric motors, a system was desired to extend automatically the cutting line from the head without interrupting cutting operations.
A most desirable automatic system would be capable of feeding cutting line as needed from the head so that line-feeding is independent of operator action during grass cutting. Structures directed toward this purpose are shown in U.S. Pats. 3,895,440, 4,020,550 and 4,035,915. These structures have in common a basket-weave supply of cutting line carried on the periphery of a disc with the line feeding from behind special post members. These post members have a cutting-abrading edge so that cutting line from the weave supply is bent about such edge in the free-traveling end portion extending into the cutting plane. The combination function of the edge, line, angular speed, etc., is arranged so that the line posts with such edge sever the free end of the cutting line when it is worn to an ineffective length. In practice, these structures are found to waste about 25 percent of the cutting line because of the excessive length of line severed at the post's edge, e.g., between one and three inches.
These structures in "automatic" line-feeding suffer a serious hysteresis, or snap-action problem. For example, these cutting heads may provide a maximum vegetation-cutting path of 18 inches. However, the cutting line may not begin to feed until it is reduced to a cutting path of ten inches. Then, the cutting line suddenly feeds to the 18-inch maximum cutting path. Besides the "start" or surprise to the operator, innocent vegetation can be unintentionally cut in what may be termed "Oops, there go the daisies", by the sudden increase in cutting path. Such automatic function can generally be termed as "snap-action line-feeders". Also, the hysteresis in the feeder mechanisms may not feed the correct line length each time to restore the maximum cutting path.
The present invention provides a rotating head with a mechanism that maintains automatically and continuously the cutting line at its maximum predetermined length extending in the cutting plane, irrespective of rates of cutting line wear or loss and magnitude of line extension.